Numerous applications, including “always-on” applications, have required mobile-broadband experience be delivered and presented to end users in a seamless fashion. When an always-on connectivity is provided by a typical radio access network (RAN), trade-offs are often encountered among characteristics such as UE power consumption, data transfer latency, network efficiency, and signaling overhead. Also, the optimum point for each trade-off could vary according to characteristics, activities, or statuses of such applications. Therefore, a specification group, also known as RAN2 which is in charge of the Radio layer 2 and Radio layer 3, has been discussing issues related to handling diverse traffic profiles in the working item eDDA (which stands for enhancements of diversity data applications) for enhancing the Long Term Evolution (LTE) communication system.
One of such current discussions involves utilization of the scheduling request (SR) which is an uplink control signaling, and its function would include requesting a UL-SCH (uplink shared channel) resource for a new transmission. FIG. 1A is a signal flow chart which illustrates using scheduling request to initiate an uplink data transfer through a typical uplink procedure. In step S111, a UE 101 may optionally receive SR configuration from an eNB 102. The SR configuration allocates resources for transferring the actual SR, and the allocation is accomplished by assigning a period between each resource for SR and a subframe offset. The SR configuration is configured by RRC signaling, particularly the sr-ConfigIndex. Currently, the possible SR periods are 1 ms, 2 ms, 5 ms, 10 ms, 20 ms, 40 ms and 80 ms. In step S112, assuming that the UE 101 wants to transmit data and consequently transmits a SR to the eNB 102. In step S113, in response to receiving the SR, the eNB 102 transmits an uplink grant which is used for transmitting a buffer status report (BSR) to the eNB 102. The uplink grant could be obtained by (blindly) decoding the physical downlink control channel (PDCCH). In step S114, the UE 101 transmits the BSR to the eNB 102. In step S115, the eNB 102 transmits an uplink grant in the PDCCH to the UE 101 for transmitting uplink packet or uplink data. In step S116, the UE 101 transmits uplink packets to the eNB 102.
The allocation of SR resources in physical uplink control channel (PUCCH) is illustrates in FIG. 1B. Assuming that the allocation of SR resources is dedicated per UE device, SR source could be named as dedicated SR resource or D-SR resource. When a UE wants to transmit uplink data, a D-SR resource could be utilized to transmit control signaling, namely the SR, in the PUCCH. In FIG. 1B, the D-SR resource could be configured in a periodic manner which would result in lesser control signaling overhead.
However, an uplink grant may also be requested through a random access procedure. For circumstances in which the D-SR resource is no longer valid due to UE time out or when the UE needs to transmit data between D-SR resources, a random access procedure could be utilized. FIG. 1C is a signal flow chart which illustrates requesting an uplink grant through a conventional random access procedure. In step S121, an UE 101 transmits a random access preamble or a sequence of predefined codes to a eNB 102 to request for a random access (RA). In step S122, in response to receiving the random access request, the eNB 102 transmits a random access response (RAR) which includes an uplink grant specifically for Msg3 to the UE 101. In step S123, the UE 101 transmits to the eNB 102 which may include a C-RNTI, and optionally user data. In step S124, in response to receiving the Msg3, the UE 101 transmits an uplink grant to the UE 101 for a RA-SR resource (i.e. SR resources allocated through RA) in order to transmit a SR.
The allocation of RA-SR resources in physical uplink control channel (PUCCH) is illustrates in FIG. 1D. It should be noted that when a UE 101 request for a uplink grant to transmits user data through a random access procedure, it would require more network resource and power consumption then using D-SR resources. For the procedure of FIGS. 1A and 1B, the UE 101 could use the semi-persistently scheduled D-SR resources to transmit the SR (S112). In this disclosure semi-persistent scheduling means that the D-SR resources are periodically scheduled, but the periodicity could be altered dynamically by a UE or a control node. For the procedure of FIGS. 1C and 1D however, step S124 needs to be finished before the UE 101 could transmit a SR. Therefore, a network could reduce control signaling overhead in favor of the semi-persistent D-SR resource scheduling.
However, according to TR36.822, simulation results have indicated that physical uplink control channel (PUCCH) utilization rate for SR (scheduling request) would most likely be very low for most traffic, especially for background traffic. Background traffic would refer to the autonomous exchanges of user plane data packets between a UE and a network generally in the absence of a specific user interaction with the device. When data traffic contains mostly sparse and small packets, such as background traffic, enhancements to efficiently allocating SR resource for such traffic has been discussed.
In one of the RAN2 meetings, one possible and simple enhancement is the introduction of longer SR periods to increase PUCCH utilization rate for SR. Since the need of SR for background traffic is infrequent, the simulation results in TR36.822 show that less than 1% SR opportunities are used for 80 ms SR period and less than 0.1% SR opportunities are used for 10 ms SR period. Due to the low SR utilization rate, it would make an intuitive sense to consider lengthening the SR period.
However, should the traffic pattern of a UE be changed dynamically, the regularly configured SR period could no longer be appropriate. One reason is that a shortened SR period could result in wasting D-SR opportunities. On the other hand, a lengthened SR period could result in longer transmission delay. Otherwise, additional random access procedures would be needed to request RA-SR resource for situations such as delivering measurements reports, transmitting data belonging to a high priority bearer, or involving delay stringent applications such as gaming. In the foreseeable future, it is very possible that wireless data capability would grow by 1000 times more than the current capacity, improving physical resource utilization rate would become necessary as methods to dynamically allocate PUCCH resource would be needed. Therefore, it would be beneficial to simultaneously consider different factors including at least but not limited to SR utilization rate, NW signaling overhead, power consumption, and corresponding SR transmission delay in order to obtain a method which may accommodate for the rapidly growth of required wireless capacity.